Cortical and subcortical correlates of functional electrical stimulation of wrist extensor and flexor muscles revealed by fMRI

Abstract

The main scope of this study was to test the feasibility and reliability of FES in a MR-environment. Functional Electrical Stimulation (FES) is used in the rehabilitation therapy of patients after stroke or spinal cord injury to improve their motor abilities. Its principle lies in applying repeated electrical stimulation to the relevant nerves or muscles for eliciting either isometric or concentric contractions of the treated muscles. In this study we report cerebral activation patterns in healthy subjects undergoing fMRI during FES stimulation. We stimulated the wrist extensor and flexor muscles in an alternating pattern while BOLD-fMRI was recorded. We used both block and event-related designs to demonstrate their feasibility for recording FES activation in the same cortical and subcortical areas. Six out of fifteen subjects repeated the experiment three times within the same session to control intraindividual variance. In both block and event-related design, the analysis revealed an activation pattern comprising the contralateral primary motor cortex, primary somatosensory cortex and premotor cortex; the ipsilateral cerebellum; bilateral secondary somatosensory cortex, the supplementary motor area and anterior cingulate cortex. Within the same subjects we observed a consistent replication of the activation pattern shown in overlapping regions centered on the peak of activation. Similar time course within these regions were demonstrated in the event-related design. Thus, both techniques demonstrate reliable activation of the sensorimotor network and eventually can be used for assessing plastic changes associated with FES rehabilitation treatment.

Figure 1

Experimental paradigm. (a) Electrode placement and maximal extent of electrically stimulated extension and flexion movement. (b) Event‐related design. 22 single extension and flexion movements of each 1 s duration were electrically elicited in an alternating pattern with an interstimulus interval lasting 17.05–21.95 s. Total duration: 900 s. (c) Block design. 6 rest and 6 stimulation blocks each lasting 21 s. The stimulation condition consisted of a repetitive extension flexion movement, stimulating alternatively WEM and WFM for 1 s. Total duration: 252 s.

Figure 2

Block design. Statistically significant activation maps FES vs. Rest (t(14) > 4.79, FDR q < 0.03 corrected). The cluster threshold was set at 10 voxels. Top row: coronar view, anterior‐posterior direction; bottom row: transversal view, superior‐inferior direction. Convention for lateralization is shown: R, right hemisphere; L, left hemisphere.

Figure 3

Event‐related design. Statistically significant activation maps FES vs. Rest (t(14) > 6.83, FDR <0.001 corrected). Top row: coronar view, anterior‐posterior direction; bottom row: transversal view, superior‐inferior direction. Convention for lateralization is shown: R, right hemisphere; L, left hemisphere.

Figure 4

Individual time courses of six subjects in five ROI in three consecutive runs within event‐related design. Color represents order of runs: 1, red; 2, green; 3, blue. Bold curves represent ROIs which have been relocated adjacent to other 2 ROIs (see text for details).